The present invention relates in general to electroerosion, and more specifically to systems and methods for monitoring and controlling an electroerosion process.
Electrochemical machining (ECM) and electrical discharge machining (EDM) are conventional processes for machining material in objects such as gas turbine components. ECM processes typically pass an electrical current in the gap between an electrode(s) and a workpiece for precision removal of amounts of material on the workpiece to achieve a desired final configuration thereof with substantially smooth surfaces. EDM processes circulate a dielectric liquid between an electrode(s) and a workpiece, and electrical discharges are generated in the gap between the electrode and the workpiece. EDM is used, for example, to drill small film cooling holes through the surfaces of turbine rotor blades and nozzle vanes.
Both ECM and EDM processes use electrical current under direct-current (DC) voltage to electrically power removal of the material from the workpiece. However, in ECM an electrolyte (an electrically conductive liquid) is circulated between the electrode(s) and the workpiece for permitting electrochemical dissolution of the workpiece material, as well as cooling and flushing the gap region therebetween. In contrast, EDM processes circulate a nonconductive (dielectric) liquid in the gap to permit electrical discharges in the gap for removing the workpiece material. As used herein, the term “electroerosion” should be understood to apply to those electromachining processes that circulate an electrolyte (electrically conductive liquid) in the gap between the electrode(s) and the workpiece, these processes enabling a high rate of material removal and reducing thermal damages to the workpiece.
Beneficially, electroerosion processes provide for quicker machining and have higher efficiencies as compared to other electromachining methods in various applications, such as, blisk roughing and machining, for example. Typically, in processes utilizing an electroerosion assembly, a voltage potential is generated across a gap between an electrode and a workpiece to be machined, resulting in an electrical discharge in the gap. According to physics of the electroerosion process, when the machining electrode (cathode) approaches the workpiece (anode) surface separated by the gap, an electrical discharge occurs through the gap due to the voltage across the electrode and the anode workpiece. The gap, which constitutes a machining zone, is filled with a liquid electrolyte medium with moderate to low electrical conductivity, and the gap allows for the flow of electrolyte, which removes eroded particles from the gap in addition to providing a suitable medium for electrical discharge or sparking for electroerosion. A “normal” electrical discharge across the gap results in desirable machining of the workpiece. An “abnormal” discharge on the other hand results in undesirable errors in machining which may have a direct repercussion on the surface finish of the machined workpiece. In some cases, the workpiece or the electroerosion assembly may be damaged due to short-circuiting because of a lack of an effective control.
Such errors can be avoided by timely and accurately monitoring of discharge patterns, detecting abnormal discharges and accordingly taking corrective measures. However, the systems currently employed in EDM for monitoring discharge patterns are generally insufficient and/or unsuitable for monitoring electroerosion processes and typically generate errors in detecting a discharge type. The errors may amount to incorrectly classifying normal discharges as abnormal and vice versa, which makes the electroerosion process susceptible to the risks mentioned above. For example, many conventional EDM assemblies employ an ignition delay detection method to determine whether a discharge is normal or abnormal. In the ignition delay detection method, discharges with an ignition delay are considered normal, whereas those without an ignition delay are considered abnormal. However, as noted above, electroerosion processes use electrolytes instead of the dielectric liquids used for typical EDM processes. Accordingly, for electroerosion processes, a number of the pulses without ignition delay are normal discharges, and the conventional ignition delay detection method improperly classifies many normal discharges as abnormal, when used to monitor electroerosion processes.
Accordingly, there exists a need for accurate detection and classification of voltage discharge in electroerosion processes. Consequently, electroerosion processes and systems with accurate monitoring and control are also desired.